Trough imatinib plasma levels are associated with both cytogenetic and molecular responses to standard-dose imatinib in chronic myeloid leukemia

Imatinib assay by high-performance liquid chromatography in tandem mass spectrometry with solid-phase extraction in human plasma

We have developed a method of liquid chromatography in tandem with mass spectrometry to monitor therapeutic levels of imatinib in plasma, a selective inhibitor of protein tyrosine kinase. After solid-phase extraction of plasma samples, imatinib and its internal standard, imatinib-D8, were eluted with Zorbax SB-C18 at 60 °C, under isocratic conditions through a mobile phase consisting of 4 mm ammonium formate, pH: 3.2 (solution A) and acetonitrile solution B. The flow rate was 0.8 mL/min with 55% solution A + 45% solution B. Imatinib was detected and quantified by mass spectrometry with electrospray ionization operating in selected-reaction monitoring mode. The calibration curve was linear in the range 10-5000 ng/mL, the lower limit of quantitation being 10 ng/mL. The method was validated according to the recommendations of the Food and Drug Administration, including tests of matrix effect (bias < 10%) and recovery efficiency (>80 and <120%). The method is precise (coefficient of variance intra-day <2% and inter-day <7%), accurate (95-108%), sensitive and specific. It is a simple method with very fast recording time (1.2 min) that is applicable to clinical practice. This will permit improvement of the pharmacological treatment of patients.

Simple methodology for the therapeutic drug monitoring of the tyrosine kinase inhibitors dasatinib and imatinib

A simple HPLC method has been developed to measure imatinib and N-desmethylimatinib (norimatinib) in plasma or serum at concentrations attained during therapy. Adaptation of this method to LC-MS/MS also allows dasatinib assay. A small sample volume (100 μL HPLC-UV, 50 μL LC-MS/MS) is required and analysis time is <5 min in each case. Detection was by UV (270 nm) or selective reaction monitoring (two transitions per analyte) tandem mass spectrometry. Assay calibration was linear (0.05-10 mg/L imatinib, 0.01-2.0 mg/L norimatinib and 1-200 µg/L dasatinib), with acceptable accuracy (86-114%) and precision (<14% RSD) for both methods. A comparison between whole blood and plasma confirmed that plasma is the preferred sample for imatinib and norimatinib assay. For dasatinib, although whole blood concentrations were slightly higher, plasma is still the preferred sample. Despite considerable variation in the (median, range) plasma imatinib and norimatinib concentrations in patient samples [1.66 (0.02-4.96) and 0.32 (0.01-0.99) mg/L, respectively, N = 104], plasma imatinib was >1 mg/L (suggested target for response) in all but one sample from patients achieving complete molecular response. As to dasatinib, the median (range) plasma dasatinib concentration was 13 (2-143) µg/L (N = 33). More observations are needed to properly assess the potential role of therapeutic drug monitoring in guiding treatment with dasatinib.

Model-based treatment optimization of a novel VEGFR inhibitor

AIM

To evaluate dosing and intervention strategies for the phase II programme of a VEGF receptor inhibitor using PK-PD modelling and simulation, with the aim of maximizing (i) the number of patients on treatment and (ii) the average dose level during treatment.

METHODS

A previously developed PK-PD model for lenvatinib (E7080) was updated and parameters were re-estimated (141 patients, once daily and twice daily regimens). Treatment of lenvatinib was simulated for 16 weeks, initiated at 25 mg once daily. Outcome measures included the number of patients on treatment and overall drug exposure. A hypertension intervention design proposed for phase II studies was evaluated, including antihypertensive treatment and dose de-escalation. Additionally, a within-patient dose escalation was investigated, titrating up to 50 mg once daily unless unacceptable toxicity occurred.

RESULTS

Using the proposed antihypertension intervention design, 82% of patients could remain on treatment, and the mean dose administered was 21.5 mg day⁻¹. The adverse event (AE) guided dose titration increased the average dose by 4.6 mg day⁻¹, while only marginally increasing the percentage of patients dropping out due to toxicity (from 18% to 20.8%).

CONCLUSIONS

The proposed hypertension intervention design is expected to be effective in maintaining patients on treatment with lenvatinib. The AE-guided dose titration with blood pressure as a biomarker yielded a higher overall dose level, without relevant increases in toxicity. Since increased exposure to lenvatinib seems correlated with increased treatment efficacy, the adaptive treatment design may thus be a valid approach to improve treatment outcome.

MicroRNA profiling in K-562 cells under imatinib treatment: influence of miR-212 and miR-328 on ABCG2 expression

BACKGROUND

Despite the enormous success of imatinib in chronic myeloid leukemia (CML), therapy resistance has emerged in a significant proportion of patients, partly because of the overexpression of ABC efflux transporters.

METHODS

Using an array comprising 667 miRNAs, we investigated whether the expression of microRNAs (miRNAs) is altered in CML K-562 cells becoming resistant to increasing concentrations of imatinib. ABCB1 and ABCG2 mRNA (quantitative real-time PCR) and protein expression (western blot) were quantified under short-term and 4 months' imatinib treatment. Interaction of miR-212 and miR-328 with ABCG2 was investigated by transfection experiments and reporter gene assays using respective miRNA precursors or miRNA inhibitors.

RESULTS

Although ABCB1 protein was not expressed, ABCG2 protein was 7.2-fold elevated after long-term treatment with 0.3 µmol/l imatinib and decreased gradually at higher concentrations. miRNAs miR-212 and miR-328 were identified to correlate inversely with ABCG2 expression under these conditions. Short-term treatment also induced ABCG2 protein concentration dependently and caused a downregulation of miR-212, but not of miR-328 at all tested concentrations (P=0.050). Reporter gene assays confirmed miR-212 to target the 3'-UTR region of ABCG2. In contrast, transfection of anti-miR-212 revealed an upregulation of ABCG2 protein expression, whereas the effect of anti-miR-328 was weak.

CONCLUSION

Our study suggests an association of imatinib treatment, miRNA downregulation and ABCG2 overexpression, possibly contributing to the mechanisms involved in imatinib distribution and response in CML therapy.

Potent mechanism-based inhibition of CYP3A4 by imatinib explains its liability to interact with CYP3A4 substrates

BACKGROUND AND PURPOSE

Imatinib, a cytochrome P450 2C8 (CYP2C8) and CYP3A4 substrate, markedly increases plasma concentrations of the CYP3A4/5 substrate simvastatin and reduces hepatic CYP3A4/5 activity in humans. Because competitive inhibition of CYP3A4/5 does not explain these in vivo interactions, we investigated the reversible and time-dependent inhibitory effects of imatinib and its main metabolite N-desmethylimatinib on CYP2C8 and CYP3A4/5 in vitro.

EXPERIMENTAL APPROACH

Amodiaquine N-deethylation and midazolam 1'-hydroxylation were used as marker reactions for CYP2C8 and CYP3A4/5 activity. Direct, IC(50) -shift, and time-dependent inhibition were assessed with human liver microsomes.

KEY RESULTS

Inhibition of CYP3A4 activity by imatinib was pre-incubation time-, concentration- and NADPH-dependent, and the time-dependent inactivation variables K(I) and k(inact) were 14.3 µM and 0.072 in(-1) respectively. In direct inhibition experiments, imatinib and N-desmethylimatinib inhibited amodiaquine N-deethylation with a K(i) of 8.4 and 12.8 µM, respectively, and midazolam 1'-hydroxylation with a K(i) of 23.3 and 18.1 µM respectively. The time-dependent inhibition effect of imatinib was predicted to cause up to 90% inhibition of hepatic CYP3A4 activity with clinically relevant imatinib concentrations, whereas the direct inhibition was predicted to be negligible in vivo.

CONCLUSIONS AND IMPLICATIONS

Imatinib is a potent mechanism-based inhibitor of CYP3A4 in vitro and this finding explains the imatinib-simvastatin interaction and suggests that imatinib could markedly increase plasma concentrations of other CYP3A4 substrates. Our results also suggest a possibility of autoinhibition of CYP3A4-mediated imatinib metabolism leading to a less significant role for CYP3A4 in imatinib biotransformation in vivo than previously proposed.

Intracellular retention of ABL kinase inhibitors determines commitment to apoptosis in CML cells

Clinical development of imatinib in CML established continuous target inhibition as a paradigm for successful tyrosine kinase inhibitor (TKI) therapy. However, recent reports suggested that transient potent target inhibition of BCR-ABL by high-dose TKI (HD-TKI) pulse-exposure is sufficient to irreversibly commit cells to apoptosis. Here, we report a novel mechanism of prolonged intracellular TKI activity upon HD-TKI pulse-exposure (imatinib, dasatinib) in BCR-ABL-positive cells. Comprehensive mechanistic exploration revealed dramatic intracellular accumulation of TKIs which closely correlated with induction of apoptosis. Cells were rescued from apoptosis upon HD-TKI pulse either by repetitive drug wash-out or by overexpression of ABC-family drug transporters. Inhibition of ABCB1 restored sensitivity to HD-TKI pulse-exposure. Thus, our data provide evidence that intracellular drug retention crucially determines biological activity of imatinib and dasatinib. These studies may refine our current thinking on critical requirements of TKI dose and duration of target inhibition for biological activity of TKIs.

Long-term outcome following imatinib therapy for chronic myelogenous leukemia, with assessment of dosage and blood levels: the JALSG CML202 study

A prospective multicenter Phase II study was performed to examine the efficacy and safety of imatinib therapy in newly diagnosed Japanese patients with chronic-phase CML. Patients were scheduled to receive imatinib 400 mg daily. Plasma imatinib concentrations were measured by liquid chromatography-tandem mass spectrometry. In 481 evaluable patients, estimated 7-year overall survival (OS) and event-free survival (EFS) at a median follow-up of 65 months were 93% and 87%, respectively. Because imatinib dosage was reduced in many patients due mainly to adverse events, subgroup analysis was performed according to the mean daily dose during the first 24 months of treatment: ≥360 mg (400-mg group; n = 294), 270-359 mg (300-mg group; n = 90) and <270 mg (200-mg group; n = 67). There were no significant differences in OS and EFS between the 300- and 400-mg groups; however, cumulative rates of complete cytogenetic and major molecular responses differed significantly between the two groups. There were no significant differences in mean imatinib trough levels between these two groups for the patients in whom trough levels had been measured. Survival and efficacy in the 200-mg group were markedly inferior to the former two groups. These results suggest that, although a daily dose of 400 mg imatinib is associated with better outcomes, 300 mg imatinib may be adequate for a considerable number of Japanese patients who are intolerant to 400 mg imatinib. Blood level monitoring would be useful to determine the optimal dose of imatinib.

Molecular resistance: an early indicator for treatment change?

Vigilant monitoring of a patient's response to current treatment is imperative to the management of chronic myeloid leukemia (CML). Early identification of treatment failure may increase the probability that alternative therapy will be effective. This review discusses the use of molecular monitoring in the timely detection of failure of imatinib treatment. Changes in the levels of BCR-ABL transcripts are predictive of response or relapse. Patients achieving a major molecular response (MMR) within 12 months of treatment may experience longer cytogenetic remission. Accumulating evidence also suggests that lower transcript levels observed ≤ 6 months after the start of treatment are associated with improved patient outcomes. For patients with primary or secondary imatinib resistance (or intolerance), dasatinib or nilotinib may be prescribed. These agents have demonstrated activity in patients harboring imatinib-resistant BCR-ABL mutations, except for the T315I substitution.

Contribution of tumoral and host solute carriers to clinical drug response

Members of the solute carrier family of transporters are responsible for the cellular uptake of a broad range of endogenous compounds and xenobiotics in multiple tissues. Several of these solute carriers are known to be expressed in cancer cells or cancer cell lines, and decreased cellular uptake of drugs potentially contributes to the development of resistance. As result, the expression levels of these proteins in humans have important consequences for an individual's susceptibility to certain drug-induced side effects, interactions, and treatment efficacy. In this review article, we provide an update of this rapidly emerging field, with specific emphasis on the direct contribution of solute carriers to anticancer drug uptake in tumors, the role of these carriers in regulation of anticancer drug disposition, and recent advances in attempts to evaluate these proteins as therapeutic targets.

Plasma exposure of imatinib and its correlation with clinical response in the Tyrosine Kinase Inhibitor Optimization and Selectivity Trial

BACKGROUND

This study evaluates the correlation between imatinib trough plasma concentrations (C(min)) and clinical response and safety in patients with newly diagnosed Philadelphia chromosome-positive chronic myeloid leukemia in chronic phase in the Tyrosine Kinase Inhibitor OPtimization and Selectivity (TOPS) trial.

DESIGN AND METHODS

Patients were randomized 1:2 to 400 mg/day or 800 mg/day imatinib. Imatinib C(min) levels were collected at pre-dose before treatment, and at the end of months 1 (day 29), 6, 9, and 12.

RESULTS

Imatinib C(min) were stable over time in the 400 mg/day dose arm, but showed a slight decrease in the 800 mg/day arm due to dose adjustments between months 1-6. The overall median imatinib C(min) levels were 1040, 1200, 1935, and 2690 ng/mL for the actual 300, 400, 600, and 800 mg/day doses, respectively. The rates of major molecular response (MMR) at 3, 6, 9, and 12 months, and complete cytogenetic response (CCyR) at 6 and 12 months were significantly lower among patients with the lowest imatinib C(min) levels at Day 29 (<1165 ng/mL, 25th percentile). There was an apparent association between high imatinib C(min) and the occurrence of grade 3/4 neutropenia and all-grade rash, diarrhea, arthralgia/myalgia, and all-cause edema. Conclusions Imatinib C(min) levels were relatively stable over time and proportional to the dose administered. Patients with an imatinib C(min) above 1165 ng/mL on Day 29 achieved MMR faster and had higher MMR and CCyR rates at 12 months. There appeared to be an association between imatinib C(min) and the frequency of some adverse events. This trial was registered at http://www.clinicaltrials.gov as NCT00124748.

Use of total and unbound imatinib and metabolite LC-MS/MS assay to understand individual responses in CML and GIST patients

OBJECTIVES

Trough total imatinib (t-IM) concentrations have been reported to be associated with therapeutic and toxic responses in patients with chronic myelogenous leukemia (CML) and gastrointestinal stromal tumor (GIST). Little is known about the relationships between effects and concentrations of either unbound imatinib (f-IM) or imatinib's major metabolite, N-desmethyl imatinib (NDI). In part, this is because of the lack of a single, validated, well-described clinically useful assay for these measurements. The authors report the development and application of such an assay.

MATERIALS AND METHODS

A single liquid-chromatography tandem-mass-spectrometry assay was used to monitor t-IM, f-IM, and t-NDI concentrations in CML and GIST patients treated at a tertiary German teaching hospital. The assay was also validated for measuring other kinase inhibitors, including t-nilotinib, sunitinib, and erlotinib. Ultrafiltration assays were validated and used to measure f-IM and to compare free fractions to plasma α1-acid glycoprotein concentrations (AGP).

RESULTS

The assays were linear over a working range (in micrograms per liter) of 8.4-8370, 8.3-4165, and 1.0-250 and had within- and between-run coefficient of variance of <7%, <12%, and <9% for t-IM, t-NDI, and f-IM, respectively. The f-IM assay was reproducible despite high (25.2%-31.6%) but concentration-independent binding to ultrafiltration devices. Clinically relevant results, such as nondetectable (ND) t-IM (<8.4 μg/L) in non-responders and >1500 μg/L in patients with major toxicity, were found. Of 156 total samples from 68 adult CML patients and 127 total samples from 42 adult GIST, only 48 samples from 22 CML patients and 40 samples from 20 GIST patients were trough samples with adequate dosing and collection information. More than half (27 of 48 CML and 24 of 40 GIST) had t-IM concentrations ≥10% below recommended target concentrations (1002 μg/L for CML and 1100 μg/L for GIST). Concentrations >50% over targets were also found in 6 of 48 CML and 4 of 40 GIST samples. Wide variations in concentrations of t-IM (range, ND to 2973 μg/L), t-NDI (range, ND to 659 μg/L), f-IM (range, 8.3-262 μg/L), and t-IM:f-IM ratios (range, 2.6%-14%) were found both between and within patients. A statistically significant association (Spearman correlation coefficient and P value for all samples, r = 0.290 and P = 0.023; for trough only, r = -0.585 and P = 0.028) was found between AGP and f-IM concentrations but wide interpatient and intrapatient variations made individual predictions unreliable.

CONCLUSIONS

The liquid-chromatography tandem-mass-spectrometry methods developed provided information useful to understand individual responses to therapy even though necessary sampling and dosing information was often not available. Wide unpredictable variations in t-IM, t-NDI, and f-IM were found. Clinical outcome trials are needed to examine whether f-IM or NDI monitoring can improve the ability to predict individual responses.

Imatinib plasma trough levels in chronic myeloid leukaemia: results of a multicentre study CSTI571AIL11TGLIVEC

Imatinib has been accepted as frontline treatment for patients with chronic myeloid leukaemia (CML), and patients generally receive doses ranging from 400 to 800 mg/day. Previous studies have demonstrated that maintaining imatinib plasma levels (IMPLs) >1000 ng/mL leads to improved responses and long-term outcomes. However, IMPLs vary among patients because of factors such as drug-drug interactions, adherence, toxicity and differential levels of expression of cellular efflux/influx proteins. In this study, IMPLs were analysed in 191 patients with CML and were compared with achievement of molecular and cytogenetic responses (CyR). IMPLs were also correlated with renal and hepatic dysfunction. Additionally, self-reported adherence was monitored. The median and mean IMPLs were 994 ng/mL and 1070 ± 686 ng/mL, respectively, with 96 patients (50%) achieving plasma levels >1000 ng/mL. Self-reported patient compliance was 98%. Patients who achieved a complete CyR (CCyR) had significantly higher IMPLs (1078 ± 545 ng/mL) than those without CyR (827 ± 323 ng/mL, p = 0.045). When grouped together, patients who achieved a CCyR or partial CyR had significantly higher IMPLs than patients who achieved a minimal CyR or did not achieve a CyR (1066 ng/mL vs 814 ng/mL, p = 0.002). There was no significant difference observed in the IMPLs between patients who achieved molecular responses (n = 177) on treatment (major molecular response, 976 ± 385 ng/mL versus complete molecular response, 1138 ± 809 ng/mL, p = 0.387). Mean IMPLs were similar in patients with or without renal or hepatic impairment. Overall, this study confirmed previous reports that higher IMPLs correlate with clinical responses and demonstrated that imatinib exposure did not differ in patients with or without liver and/or renal dysfunction. The use of IMPL testing and patient diaries may be practical tools for the management of imatinib therapy in patients with CML.

Imatinib trough plasma levels do not correlate with the response to therapy in patients with chronic myeloid leukemia in routine clinical setting

Association of trough imatinib plasma levels (IPL) with cytogenetic or molecular response to treatment in patients with chronic myeloid leukemia (CML) was repeatedly reported. We analyzed their value in the routine clinical setting in 131 patients with chronic phase CML in whom imatinib was applied as first- or second-line treatment. A total of 1,118 measurements were obtained by ultra-performance liquid chromatography-tandem mass spectrometry assay in patients treated with daily dose of imatinib ranging from 100 to 800 mg. Samples were obtained from 1 to 96 h after drug ingestion. High inter (36%) and intraindividual variability (9-33%) of IPL was observed. For analysis of correlation of IPL with treatment response, two sets of samples were selected according to the European LeukemiaNet (ELN) criteria. The first set consisted of 241 samples taken 24 ± 2 h after dosing in 54 patients, and the second one consisted of 329 samples taken 24 ± 4 h after imatinib ingestion in 84 patients. In both sets, only patients treated with 400 mg imatinib once daily for at least 18 months were included. From multiple measurements in individual patients, mean IPL were used. In both sets, we were not able to demonstrate a statistically significant correlation between IPL and response to treatment according to the ELN. We believe that this was due to the differences in patients' compliance, leukemia biology, and other variables that are difficult to eliminate in the routine clinical practice. The use of IPL for prognostic estimation in CML treatment outside the clinical trials is probably limited.

Population pharmacokinetic and exposure-response analysis of nilotinib in patients with newly diagnosed Ph+ chronic myeloid leukemia in chronic phase

PURPOSE

We investigated the population pharmacokinetics and exposure-response relationship of nilotinib in patients with newly diagnosed chronic myeloid leukemia (CML) in chronic phase.

METHODS

Nilotinib was given at 300 mg or 400 mg twice daily. Serum concentration data (sparse and full pharmacokinetic profiles) were obtained from 542 patients over 12 months. A population pharmacokinetic analysis was performed using nonlinear mixed-effect modeling. Exposure-response relationships were explored graphically or using logistic regression models.

RESULTS

Nilotinib concentrations were stable over 12 months. Patients in the 400 mg twice-daily arm had an 11.5% higher exposure than did those in the 300 mg twice-daily arm, and the relative bioavailability of nilotinib 400 mg twice daily was 0.84 times that of 300 mg twice daily. Patient demographics did not significantly affect nilotinib pharmacokinetics. The occurrence of all-grade total bilirubin elevation was significantly higher in patients with higher nilotinib exposure, and a positive correlation was also observed between nilotinib exposure and QTcF change on electrocardiograms from baseline. There was no significant relationship between nilotinib exposure and major molecular response at 12 months.

CONCLUSIONS

There is a less than proportional dose-exposure relationship between nilotinib 300 mg and 400 mg twice-daily doses. Blood level testing is unlikely to play an important role in the general management of patients with newly diagnosed CML treated with nilotinib.

Chronic phase chronic myeloid leukemia patients with low OCT-1 activity randomized to high-dose imatinib achieve better responses and have lower failure rates than those randomized to standard-dose imatinib

BACKGROUND

The functional activity of the organic cation transporter 1 (OCT-1) protein (OCT-1 activity) is an excellent predictor of molecular response and progression-free survival in patients with newly diagnosed chronic phase chronic myeloid leukemia treated with imatinib as front-line therapy.

DESIGN AND METHODS

In this study the predictive value of OCT-1 activity in patients treated with imatinib 400 mg/day or 800 mg/day was evaluated in relation to trough imatinib plasma levels assessed in 100 patients enrolled in the Tyrosine Kinase Inhibitor Optimization and Selectivity (TOPS) trial.

RESULTS

The rate of major molecular responses by 24 months in patients on imatinib 400 mg/day was significantly higher in those with high OCT-1 activity than in those with low OCT-1 activity (low OCT-1 activity, 57% of patients; high OCT-1 activity, 100%; P < 0.001); the corresponding difference in patients treated with imatinib 800 mg/day did not reach statistical significance (low OCT-1 activity, 68%; high OCT-1 activity, 95%; P = 0.073). In addition, the combination of low trough imatinib levels (< 1200 ng/mL) and low OCT-1 activity defined a group of patients who had the lowest rates of major molecular response (47%) by 24 months compared to all other patients (81%, P = 0.009). These patients were also at the highest risk of failed imatinib therapy when compared to all other patients (P<0.001).

CONCLUSIONS

High-dose imatinib leads to superior molecular responses in patients with low OCT-1 activity. In this group trough imatinib levels may define a group with inferior outcomes. Among patients with high OCT-1 activity, neither higher imatinib dose nor monitoring imatinib trough levels was found to be of significant clinical value. Hence OCT-1 activity determined prior to the start of therapy in newly diagnosed CML patients provides a valuable prognostic tool to determine the optimal up-front dose of imatinib in patients with newly diagnosed chronic phase chronic myeloid leukemia.

Tyrosine kinase inhibitors induced immune thrombocytopenia in chronic myeloid leukemia?

The outcome and quality of life of chronic myeloid leukemia (CML) patients has remarkably changed with the treatment of tyrosine kinase inhibitors (TKIs). Currently, hematopoietic stem cell transplantation (HSCT) is considered mainly as a third line salvage therapy in cases of TKIs resistance or intolerance. Here we describe a patient with chronic phase CML who developed both resistance and late occurrence of s severe thrombo-cytopenia on first and second generation TKIs and eventually underwent HSCT. Although the mechanism of the myelosuppression is not fully understood, we showed for the first time the development of dose dependent platelet antibodies in the presence of TKIs, suggesting the possibility of TKIs induced thrombocytopenia. Our case emphasizes that late development of severe myelosuppression during imatinib treatment is probably an important indication for consideration of early HSCT.

[Pharmacokinetics and impaired organic functions]

The interindividual variability in pharmacokinetics represents one of the factors involved in difference of both efficacy and toxicity of anticancer drugs prescribed to patients with the same cancer disease. The causes of pharmacokinetic interindividual variability are themselves divers. The impaired organic function corresponding either to liver or kidneys represents the major cause since any impaired function is systematically responsible of pharmacokinetic modifications, and due to the amplitude of these modifications. In this article, the clinically relevant pharmacokinetic parameters are shown. The methodologies used to study the pharmacokinetic variability due to impaired organic functions and to control them are detailed.

Genetic determinants of anticancer drug activity: towards a global approach to personalized cancer medicine

While current trials of anticancer agents serve to provide a population-based validation of therapeutic activity, clinical success is typically restricted to tumors of select molecular subtype. Recent insights have yielded a growing catalogue of germline and tumor-based aberrations that can predetermine whether a patient will achieve clinical benefit from a drug or not. Thus, in order to realize the true potential of anticancer agents, we need to define the molecular contexts under which they will prove both efficacious and safe. In this article, we provide an overview of such molecular determinants and introduce the concept of 'cancer patient profiling' - the process and science of defining the optimal therapy for a given patient through the generation and analysis of system-wide molecular information.

Predicting the response of CML patients to tyrosine kinase inhibitor therapy

As of 2011, the choice of tyrosine kinase inhibitor (TKI) for the patient with newly diagnosed chronic-phase chronic myelogenous leukemia (CP-CML) is no longer limited to imatinib but can be expanded to include nilotinib and dasatinib. Since 2000, imatinib has demonstrated remarkable efficacy in the majority of chronic-phase patients. Nilotinib and dasatinib, both more potent TKIs, are likely to produce quicker and deeper molecular responses, but there are no established criteria for choosing the best inhibitor for each patient. We now need to establish clearly defined recommendations to address this new stage, in which individualized therapy in the front-line should become a reality. Likely to be paramount in this setting are assays that directly assess the efficacy of the protein-drug and drug-transporter interactions, taking into account factors intrinsic to the patient, factors related to disease stage, and the amount of drug freely available in the plasma.

Evolving treatment strategies for patients newly diagnosed with chronic myeloid leukemia: the role of second-generation BCR-ABL inhibitors as first-line therapy

In patients with chronic myeloid leukemia (CML), disease in the initial chronic phase (CP) and subsequent progression are driven by the oncogenic activity of the BCR-ABL fusion kinase. Imatinib, a tyrosine kinase inhibitor of BCR-ABL, has been the mainstay of first-line therapy for CML for 10 years. Although patients with CML-CP respond well to imatinib, those who have delayed reductions in leukemic burden during imatinib therapy, such as not achieving a complete cytogenetic response (CCyR) by 12 months, have an increased risk of disease progression. It has been recognized, with 8 years of observation, that patients who achieve an early major molecular response (MMR) on imatinib have a very low probability of disease progression. Recent randomized phase 3 trials have shown that first-line treatment with dasatinib or nilotinib-more potent BCR-ABL inhibitors-results in significantly higher rates and more rapid achievement of CCyR and MMR in comparison with standard-dose imatinib. These trials suggest that CML treatment can be improved with more potent BCR-ABL inhibition during initial therapy, but further follow-up is needed to confirm that the improved response rates with dasatinib and nilotinib are maintained long term.

High-dose imatinib for newly diagnosed chronic phase chronic myeloid leukemia patients--systematic review and meta-analysis

Imatinib at a dose of 400 mg daily is considered frontline treatment in chronic phase chronic myeloid leukemia (CP-CML). We conducted a systematic review and meta-analysis of randomized controlled trials comparing frontline treatment with imatinib 400 mg daily versus higher doses (≥600 mg daily) in patients with CP-CML. The search yielded four trials, randomizing 1,673 patients. At 12 months, high dose compared with standard dose imatinib improved complete cytogenetic response (CCyR) (RR 1.17, 95% CI 1.08-1.26, four trials, I(2) = 33%) as well as major molecular response (MMolR) (RR 1.26, 95% CI 1.12-1.42, four trials, I(2) = 0%). There was no difference in all-cause mortality or disease progression at the end of follow up. Adverse events requiring discontinuation were more common in the high-dose arm (RR 1.98, 95% CI 1.20-3.26, three trials, I(2) = 0%), as were Grade III/IV neutropenia and thrombocytopenia: RR 1.56, 95% CI 1.15-2.12 and RR 1.86, 95% CI 1.28-2.70, respectively. There is currently insufficient evidence to support the routine use of higher doses of imatinib as frontline treatment for CP-CML. Extended follow up is needed to evaluate if the superior CCyR and MMolR with higher doses of imatinib will translate to long-term clinical benefit.

Measuring response to BCR-ABL inhibitors in chronic myeloid leukemia

In patients with chronic myeloid leukemia (CML), the hallmark Philadelphia chromosome is the marker of disease that can be detected by conventional metaphase cytogenetics, fluorescence in situ hybridization, or polymerase chain reaction. The current "gold standard" of treatment response is cytogenetic response. Cytogenetic response to imatinib is strongly associated with disease progression and survival. Various strategies aimed at improving cytogenetic response have been explored, such as escalation of imatinib and switching to the newer breakpoint cluster region/v-abl Abelson murine leukemia viral oncogene (BCR-ABL) inhibitors dasatinib and nilotinib. Data from recent randomized trials of dasatinib and nilotinib as first-line therapy of newly diagnosed chronic-phase CML suggest that these agents are more effective than imatinib in achieving 6-month and 12-month complete cytogenetic responses. However, it is still too early to know whether or not this early response will translate into a long-term survival advantage. In addition, more sensitive assays to detect residual disease also may be associated with improved long-term outcomes. The deepest measure of response-a complete molecular response-may help identify patients who can stop taking imatinib for the short term, although the long-term consequences of this strategy remain unknown.

The controversial role of the Hedgehog pathway in normal and malignant hematopoiesis

Hedgehog (Hh) is a developmental signaling pathway in which Hh ligands bind Patched (Ptch), which relieves its inhibition of Smoothened (Smo), allowing the Gli family of transcription factors to translocate to the nucleus and activate Hh target genes. The role of Hh signaling in hematopoiesis is controversial and ill defined. Although some groups observed self-renewal defects with decreased replating and reduced efficiency of secondary murine transplants, other groups reported no hematopoietic phenotypes, which may be related to the timing of Hh abrogation. In malignant hematopoiesis, most attention has been focused on the role of Hh signaling in chronic myeloid leukemia (CML), considered by many to be a stem cell disorder that bears the constitutively active BCR-ABL tyrosine kinase. Despite the elimination of most leukemia cells through BCR-ABL inhibition, most patients remain PCR positive, suggesting that the putative CML stem cell may be resistant to kinase antagonism. Groups are now exploring the Hh pathway as an alternate pathway supporting CML stem cell survival. Knockdown or inhibition of Smo abrogates or delays the appearance of CML in several in vitro and in vivo models. These data have lead to clinical trials using BCR-ABL kinase and novel Smo inhibitors in combination.

Lapatinib in breast cancer - the predictive significance of HER1 (EGFR), HER2, PTEN and PIK3CA genes and lapatinib plasma level assessment

BACKGROUND

Breast cancer treatment trends are currently based on tailored therapies using tumor and patient biomarkers. Lapatinib is the first dual inhibitor of HER1 (EGFR, ErbB1) and HER2 (ErbB2, Neu) tyrosine kinases to be used in clinical practice. However, only HER2 is currently used for therapy indications and new predictors for the treatment with lapatinib are sought.

METHODS AND RESULTS

This minireview focuses on lapatinib and its role in breast cancer treatment. Preclinical and clinical studies as well as pharmacological characteristics are briefly reviewed while the focus is on efficacy assessment including predictive factors for therapy outcome.

CONCLUSION

Lapatinib (Tykerb/Tyverb) was Food and Drug Administration (FDA) approved in 2007 for use in combination with capecitabine for the treatment of HER2-positive advanced or metastatic breast cancer in patients who had received previous treatment (including anthracycline, taxane and trastuzumab containing regimens) and in 2010 for use in combination with letrozole for postmenopausal women with hormonal receptor positive and HER2- positive metastatic breast cancer. In contrast to trastuzumab (Herceptin), lapatinib is orally administered and it targets both HER2 and HER1 receptors. As a synthetic and oral tyrosine kinase inhibitor (TKI), it is convenient, cheaper and easier to produce than monoclonal antibodies. The recommended dosage is not dependent on body weight either. Lapatinib plasma level measurement could be an approach to tailored therapy for further optimizing the dose and prolonging this efficient therapy. New lapatinib response predictors are being evaluated. At this time, only HER2 amplification/overexpression is used to choose lapatinib therapy candidates. Further studies on concurrent HER1 fluorescent in situ hybridization (FISH)/immunohistochemistry (IHC) assessment and/or microarray analyses may produce new data on the predictive role of the HER1 (EGFR) gene/protein. PTEN loss and PIK3CA gene mutations are other markers that may predict lapatinib poor response.

Pharmacokinetic impact of SLCO1A2 polymorphisms on imatinib disposition in patients with chronic myeloid leukemia

The purpose of this study was to explore the role of the organic anion-transporting polypeptide (OATP) 1A2, which is encoded by SLCO1A2, in the cellular uptake of the Bcr-Abl tyrosine kinase inhibitor imatinib, and the relationship between SLCO1A2 polymorphisms and the pharmacokinetics of imatinib in patients with chronic myeloid leukemia (CML). Imatinib uptake was significantly enhanced in OATP1A2-transfected human embryonic kidney (HEK) 293 cells (P = 0.002). Naringin, an OATP1A2 inhibitor, decreased the transport of imatinib in OATP1A2-transfected HEK293 cells, the human intestinal cell line Caco-2, and K562 CML cells. Linkage disequilibrium was found between the SLCO1A2 -1105G>A and -1032G>A genotypes in 34 CML patients and 100 healthy subjects. Imatinib clearance in CML patients was influenced by the SLCO1A2 -1105G>A/-1032G>A genotype (P = 0.075) and the SLCO1A2 -361GG genotype (P = 0.005). These findings suggest that imatinib is transported into cells by OATP1A2, and that SLCO1A2 polymorphisms significantly affect imatinib pharmacokinetics.

Metronidazole leads to enhanced uptake of imatinib in brain, liver and kidney without affecting its plasma pharmacokinetics in mice

Objectives

The pharmacokinetic interaction between metronidazole, an antibiotic–antiparasitic drug used to treat anaerobic bacterial and protozoal infections, and imatinib, a CYP3A4, P-glycoprotein substrate kinase inhibitor anticancer drug, was evaluated.

Methods

Male imprinting control region mice were given 50 mg/kg imatinib PO (control group) or 50 mg/kg imatinib PO, 15 min after 40 mg/kg PO metronidazole (study group). Imatinib plasma, brain, kidney and liver concentrations were measured by HPLC and non-compartmental pharmacokinetic parameters estimated.

Key findings

Metronidazole coadministration resulted in a double-peak imatinib disposition profile. The maximum concentration (Cmax) decreased by 38%, the area under the curve (AUC0–∞) decreased by 14% and the time to Cmax (Tmax) was earlier (50%) in plasma. Apparent volume of distribution (VSS/F) and oral clearance (Cl/F) increased by 21% and 17%, respectively. Imatinib tissue penetration was higher after metronidazole coadministration, with 1.7 and 2.1-fold AUC0–∞ increases in liver and kidney, respectively. Metronidazole increased imatinib's tissue-to-plasma AUC0–∞ ratio in liver from 2.29 to 4.53 and in kidney from 3.04 to 7.57, suggesting higher uptake efficiency. Brain Cmax was 3.9-fold higher than control and AUC0–t last was 2.3-fold greater than plasma (3.5% in control group). No tissue-plasma concentration correlation was found.

Conclusions

Metronidazole slightly decreased imatinib systemic exposure but enhanced liver, kidney and brain penetration, probably due to metronidazole-mediated inhibition of P-glycoprotein and other efflux transporters. The high brain exposure opens possibilities for treatment of glioma and glioblastoma. Renal and hepatic functions may need to be monitored due to potential renal and hepatic toxicity.

Association of SLCO1B3 polymorphism with intracellular accumulation of imatinib in leukocytes in patients with chronic myeloid leukemia

Intracellular concentration of imatinib in leukemic cells is thought to affect the clinical efficacy of this drug in patients with chronic myeloid leukemia (CML); however, there is no report that directly indicates the relationship between intracellular concentration and clinical outcome and/or, plasma concentration. In addition, the impacts of genetic variations of drug transporters, which mediate leukocyte concentration of imatinib, are unknown. In the present study, we investigated the correlation between intracellular imatinib concentrations in leukocytes, plasma imatinib levels, and genotypes of drug transporters, including ATP binding cassette B1 (ABCB), ABCG2, solute carrier 22A1 (SLC22A1), solute carrier organic anion transporter family members 1B1 (SLCO1B1) and SLCO1B3. The imatinib levels in leukocytes were determined using HPLC in 15 patients with chronic phase CML. No significant correlation between intracellular and plasma concentrations of imatinib was observed. The intracellular concentration was comparable in both patients with or without complete cytogenetic response. The intracellular imatinib concentration was significantly higher in patients with SLCO1B3 334TT than in those with 334TG/GG (p=0.0188). Plasma concentrations were similar in both SLCO1B3 genotypes (p=0.860), thereby resulting in the intracellular to plasma concentration ratio being higher in patients with SLCO1B3 334TT than those with 334 TG/GG (p=0.0502). These results suggested that the SLCO1B3 334T>G polymorphism could have a significant impact on the intracellular concentration of imatinib in leukocytes as a promising biomarker for personalized treatment of CML patients.